The prior art includes numerous types of devices for aligning a gun sight in accurate relation with the gun bore. Light-emitting devices have been used which direct a beam of light through the bore of the firearm onto a target so that the bore can be aligned with the target. One such light-emitting alignment device is disclosed in U.S. Pat. No. 4,530,162, issued July 23, 1985 to Forrest et al., wherein a light-generating device is rigidly secured to the chamber end of a rifle, and a muzzle assembly is mounted in the muzzle end of the barrel. The light is directed through a first tubular extension where it is reflected by a 45-degree mirror which is mounted in a chamber elbow into a second tubular extension which is mounted in the gun barrel. The chamber elbow must be precision machined to be snugly fitted into the chamber and both of the extensions must have accurately machined bores therethrough for alignment with perpendicular bores in the chamber elbow. It is also apparent that attachment means must be provided for securing the assembly in the receiver.
Another type of boresighting method that uses light-emitting devices is disclosed in U.S. Pat. No. 3,782,832, issued Jan. 1, 1974, to Hacskaylo. In this patent, an aiming light is mounted in a boresight mechanism which is mounted to the weapon. A light source is secured in a canister, and the canister is mounted in the breech of the firearm. The operator aligns and positions the aiming light with respect to the boresight light beam. A head-worn viewing scope is used by the operator to observe the positions of the boresight light and the aiming light that is reflected off a target.